Cathode ray tube



Patented Oct. 22, 1940 UNITED STATES CATHODE RAY TUBE Frederick Hermes Nicoll, Ickenham, England, as-

signor to Electric & Musical Industries Limited, Hayes, Middlcscx,vEngland, a company of Great Britain Application November 1s,- 1938, serial No. 241,092 y In Great Britain November 19, 1937 3 Claims.

This invention relates to cathode ray tubes of the kind that are used for the generation of electrical signals for television transmission, for the reproduction of such signals and for use in 5. cathode ray oscillographs and for other purposes.

In cathode ray tubes of this kind a beam of electrons is generated in a cathode ray gun comprising a cathode and several additional electrodes which are employed for a variety of purposes, such as for screening the cathode, for focussingr the electroncbeam, for modulating the electron beam and for other purposes depending upon the type of cathode ray tube to which the gun is ap- ,15 plied. In all cases it is necessary to mount the gun co-axially with respect to the neck of the cathode ray tube and such operation kentails considerable diiculty if the gun is to be accurately centered. The neck of the cathode ray tube in which the gun is mounted is usually formed portion of the envelope and it is found dinicult to obtain glass tubing of suciently accurate internal dimensions to enable the gun to bel 135 The object of the present invention is to provide an improved cathode ray tube whereby the gun can be more easily and accurately centered in the neck of the tube. According to one feature of the present invention there is provided 40 a glass envelope for a cathode ray tube the neck of which is provided with internal depressions such that in any given plane perpendicular to the axis oi the neck the distances of the internal depressions from the center of the neck are sub- 45 stantially constant for accurately and rigidly aligning the cathode ray gun structure in said neck.

In order that the present invention may be clearly understood and readily carried into ef- 50 fect it will now be described with reference to the accompanying drawing which illustrates embodiments of the present inventionby Way of example and in which:

Figure 1 illustrates a longitudinal section 55 through a portion of a cathode ray tube,

(cresci-141) of glass tubing which is attached to the other Figure 2 illustrates an end-view taken in the plane 2-2 of Figure '1,

Figure 3 illustrates a longitudinal section of a portion of the neck ofr a cathode ray tube.

Figures 4 and 5 illustrate plans of spacing elea ments, used for engaging the gun structurefwith the depressions in the tube. Y.

Figure 6 illustrates a longitudinal section through a modified form of glass envelope for acathode ray tube; 1 l 1-0;

In Figure l the neck of a cathode ray tube lI has angularly spaced depressions 3 formed thereon, these depressions being formed in two setsl which are spaced longitudinally apart with respect to each other. Inserted in the neck of the f5; tube is the cathode ray gun structure having insulating or spacing elements 4, which may beY rnica discs, tWo of which spacing elements engage with the depressions 3 in the neck.

In the embodiment illustrated in Figures 1 and 2, the insulating element 4 in the plane 2-2 $20 which engages With the depressions 3, hasdepressions 5 formed therein which are of such dimensionsl so that the shoulder of the depression 5 fits fairly closely about the shoulder of the depressions 3 in the neck so as .to tend to prevent rotational movement of the gun structure in the tube. The depressions 3 in the tube, formed according to one feature of the'present invention, have a substantially uniform internal diameter so that the insulating elements #l may 30 be readily fashioned to engage accurately therewith. In the embodiment shown, thel depressions are spaced angularly apart at 'angles of 120 degrees Awith each other.

The insulating elements 4 of lthe gun struc- 35 ture are provided with holes 6 therein through which are riveted short supporting elements' for, the supporting rods 'l which run substantially the length of the gun. The cathode of the gun, Which may be an indirectly heated element, has 40 a screening electrode 8 in the form of a longitudinal cylinder,A the cylindrical electrode being provided With a shaped metal disc 9 in the region' of the plane 2,-2, the insulating element 4 being riveted to this shaped metal disc 9 by 'F45 rivets l0.

The internal diameter between the depressions 3 being substantially uniform provides means for accurately positioning the gun with respect tothe tube by the engagement of the 50 insulating elements and the depressions, the insulating elements being readily fashioned to engage With said depressions'. The engagement between the insulating elements and the depressions may be in the nature of a push fit, or 5,5

of said insulating elements and the depressionsI in the tube may be such as to tend to preventA rotational movement of the gun structure in the tube, While the engagementl of one or vmore other` of said insulating elements` with" said depres-f l5 sions may be such .as to tend'toprevent longitudinal movement of the gun structure with resuect to the tube.

The gun structure is thus firmlyfsupported.infy

the neck and the use of the usual band around the pinch or reentrant neck portion of the tube for supporting the gun structure may be dispensed with. The pinch of the envelope through which the conducting 'leads to the various electrodes of the gun extend may be relieved of one of its usual functions of supporting the gun, the Support for the latter being effected due to the engagement of the insulating elements with the said depressions and with such a construction, the conducting leads may be brought out at the periphery of the neck of the tube, as at I4, Figure l, and a ring pinch maybe used for sealing off the end of the neck of the tube. The leads which are connected to the pinch may serve to prevent relative rotational movement between the I gun and the neck of the tube.

. The glass tubing employed in the construction of the cathode ray tube is preferably mouldblown and the depressions may be formed inthe tubing after the tubing is formed and prior to (40 the connection of the tubing of the other portion of the envelope of the cathode ray tube. The depressions may be formed by locally heating the tubing in the region where the depressions are to bev formed so that the tubing contacts with a cy- T215 lindrical former preferably of metal which has been inserted into the neck, the depressions being formed by the application of pressing tools to the outer surface of the tubing. Since the former is cylindrical, the inner surfaces of the 50, depressions are cylindrical and co-axialwith the tubular neck, and elemental areas of the inner surfaces of the depressions are equi-distant from the longitudinal axisof the tubing. After the depressions are formed the tubing is annealed.

55 In Figure 3 is illustrated a portion of a neck of a cathode ray tube which is provided with a depression 3 therein, which depression is provided with a further depression II therein. The depression II is preferably of substantially V- i60 shape. By providing an insulating or spacing element of the gun structure with suitably shaped projections I3as shown in Figure 4, these latter may be made to engage with the further depressions II, and such engagement will tend to prevent longitudinal movement of the gun structure with respect to the tube.

A construction of insulating or spacing element is illustrated in Figure 4 wherein the insulating .70 element has generally an external diameter to correspond with the internal diameterv of the tube between the depressions but is provided with projecting lugs I3, which projecting lugs are arranged to engage with additional depressions suc-h as Iii, Figure 3. The outer edges of the lugs I3 are preferably arranged accurately to engage the apices of the further depressions II.

A modified form of insulating or spacing element is illustrated in Figure 5. The insulating element here illustrated is cam-shaped, having 5 a. maximum diameter at certain points thereof which vgradually-'decreases to'a minimum, and atthese points increases' to a"m'aximum again,

a series of projecting edges I2 thus being formed.

The mica disc illustrated in Figure 5 is formed 10 with three projecting edges I2 spaced so as to be substantially equi-.distant around the periphery, the minimum external diameter of the disc so formed. being too small to contact with the depressions inthe neck of the tube, while the maxi- 15 mum external diameter of the disc so formed is greater than the internal diameter of the tube with the depressions therein. A cathode ray gun structure embodying such a spacing element may thus be readily inserted into the tube and ro- 20 tated until the'spacing element" contacts firmly withthe depressions formed in the tube. The use of such a spacing element is advantageous when the tube is often dismantled and reassembled as diierent parts of the periphery of the mica disc, 25 which tend to become damaged by such treatment, maybe employedffor ensuring rigid m'ountingo-f the gun structure. It-has been found that a'suitable length for a projecting edge such as I2 is 0.01 inch used with a tube having an inter- 30 nal diameter of about 1.5 inches.

In the modified formy of glass envelope for a cathode ray tube' illustrated in Figure 6, the neck portion I a is of a substantially cylindrical shape and the depressions 3a formed in the neck por- 35 tion are in the form of truncatedA cones, the method of forming the depressions according to one feature of the present invention ensuring that ina given plane perpendicular to the axis of the neck the distances of the internal depres- (40 sions from the centre of the neck are substantially constant. The depressions 3a may be portions ofthe same concor may be different truncated cones. Further, the neck portion Ia need not be substantially cylindric-aLbut may be sub- F Stantially conical, and'have conical depressions formed therein where the depressions 3aV are formed. The formeremployed fin the construction of such a glass envelope for a cathode ray tube may be in the form of a cone, or may be 650 conical with suitable projections thereornor may be in the form of a cylinder having projections thereonin the form ofv truncated cones. The insulating or spacing elements employed with such a modified` form of glassenvelope may be suitably dimensioned to fit into the projections 3a, While the gun structure used may be of the usual' form.

Whilst it has been found preferable to provide longitudinally extended depressions, it will `be unf6() derstoocl that, if desired, `the depressions may be of annular form, that is to say, they may eX- tend around the circumference of the tubing, in which case two or moreof said annular' depressions will be provided, the number of depressions 455 preferably corresponding to the number of'mica discs employed in the gun.

Tubes made according to the present invention are found to have internal diameters which generally conform with each other to an accuracy ,'70

of one to twothousandths of anfinoh in a tube having an internal vdiameter of the order of one and a half inches, so that it is seen that the present invention providestubes ofextremely accurate internal dimensions andiinwhich, therefore, 75

the gun structure may be accurately and rigidly aligned.

I claim:

l. An envelope for a cathode ray tube having a tubular section, a plurality of narrow depressions running lengthwise of a portion of said tubular section, the inner surfaces of said depressions being cylindrical and substantially co-aXial with said tubular section and the distances between the inner surfaces of said depressions and the longitudinal aXis of said tubular section being substantially equal over the length of said depressions.

2. In combination, a cathode ray tube having an envelope one section of which is tubular, three equally spaced depressions around the tubular section, said depressions running lengthwise of a portion of said tubular section, the inner surfaces of said depressions being concentric with said section which is tubular and the distances between the inner surfaces of said three equally spaced depressions and the longitudinal axis of said tubular section being substantially equal over vthe length of the depressions, a plurality of resilient electrode supports supported transversely of said longitudinal axis solely by said depressions at a plurality of separated points along the length of said depressions and a mount structure supported axially of said tubular section by said electrode supports and by said depressions.

3. In combination, a cathode ray 'tube having an envelope a portion of which is tubular, a plurality of depressions in said tubular portion equally spaced about said tubular portion, a second plurality of depressions equally spaced about and in said tubular portion but displaced length- Wise along said tubular portion from the firstmentioned depressions, an electron gun structure within the tubular portion of said envelope and a plurality oi spacers on said gun structure, at least one of Which is in contact with said rst-mentioned depressions and another of which is in contact With said second plurality of depressions to support the electron gun structure centrally of said tubular portion.

FREDERICK HERMES NICOLL. 

